U.S. patent application number 13/706194 was filed with the patent office on 2014-06-05 for exhaust humidity sensor.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Timothy Clark, Stephen B. Smith, Richard E. Soltis, Gopichandra Surnilla, Jacobus Hendrik Visser.
Application Number | 20140156172 13/706194 |
Document ID | / |
Family ID | 50726278 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140156172 |
Kind Code |
A1 |
Surnilla; Gopichandra ; et
al. |
June 5, 2014 |
EXHAUST HUMIDITY SENSOR
Abstract
Embodiments for adjusting engine operating parameters based on
output from an exhaust humidity sensor are provided. One example
method for an engine comprises based on a dew point of exhaust gas,
adjusting an exhaust gas sensor heater configured to heat an
exhaust gas sensor disposed in an exhaust passage of the engine,
the dew point based on output from a humidity sensor disposed in
the exhaust passage.
Inventors: |
Surnilla; Gopichandra; (West
Bloomfield, MI) ; Soltis; Richard E.; (Saline,
MI) ; Visser; Jacobus Hendrik; (Farmington Hills,
MI) ; Smith; Stephen B.; (Livonia, MI) ;
Clark; Timothy; (Livonia, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearbrom |
MI |
US |
|
|
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
50726278 |
Appl. No.: |
13/706194 |
Filed: |
December 5, 2012 |
Current U.S.
Class: |
701/104 ; 60/274;
701/102; 73/29.02 |
Current CPC
Class: |
F01N 11/00 20130101;
F01N 2560/02 20130101; Y02T 10/47 20130101; G01N 19/10 20130101;
F02D 2041/1472 20130101; F01N 2560/022 20130101; Y02T 10/40
20130101; F01N 2560/026 20130101; F01N 2560/028 20130101; F01N
2560/20 20130101; F01N 2560/025 20130101; F02D 41/1454
20130101 |
Class at
Publication: |
701/104 ;
701/102; 60/274; 73/29.02 |
International
Class: |
F01N 11/00 20060101
F01N011/00; G01N 19/10 20060101 G01N019/10 |
Claims
1. A method for an engine, comprising: based on a dew point of
exhaust gas, adjusting an exhaust gas sensor heater configured to
heat an exhaust gas sensor disposed in an exhaust passage of the
engine, the dew point based on output from a humidity sensor
disposed in the exhaust passage.
2. The method of claim 1, wherein adjusting the exhaust gas sensor
heater further comprises deactivating the exhaust gas sensor heater
if the dew point is greater than a temperature of the exhaust gas
sensor.
3. The method of claim 1, wherein adjusting the exhaust gas sensor
heater further comprises activating the exhaust gas sensor heater
if the dew point is less than a temperature of the exhaust gas
sensor and exhaust gas temperature is below a threshold.
4. The method of claim 1, further comprising adjusting a fuel
injection amount based on output from the humidity sensor.
5. The method of claim 1, further comprising adjusting exhaust gas
temperature based on output from the humidity sensor.
6. The method of claim 1, wherein the dew point is determined based
on relative humidity of the exhaust gas determined by the humidity
sensor, exhaust gas temperature, and exhaust gas pressure.
7. A method for an engine, comprising: determining a light-off
temperature of a catalyst disposed in an exhaust passage of the
engine based on exhaust gas water content measured by a humidity
sensor disposed in the exhaust passage downstream of the catalyst;
and during cold start conditions, adjusting engine operating
parameters to increase exhaust gas temperature above the light-off
temperature.
8. The method of claim 7, wherein determining the light-off
temperature further comprises: during engine cold start conditions,
predicting an amount of water to be released from the catalyst when
the catalyst reaches light-off temperature; and setting the
light-off temperature as an exhaust gas temperature at which the
predicted amount of water is released from the catalyst.
9. The method of claim 8, further comprising determining that the
predicted amount of water has been released from the catalyst based
on output from the humidity sensor.
10. The method of claim 8, wherein the predicted amount of water to
be released from the catalyst is estimated based on an amount of
exhaust gas constituents stored in the catalyst during cold start
conditions.
11. The method of claim 7, wherein adjusting engine operating
parameters to increase exhaust gas temperature further comprises
adjusting air-fuel ratio.
12. The method of claim 7, wherein adjusting engine operating
parameters to increase exhaust gas temperature further comprises
retarding spark timing.
13. A method for an engine having a catalyst, comprising: adjusting
a measured exhaust gas water content based on water storage and
release in the catalyst; and adjusting a fuel injection amount
based on the adjusted exhaust gas water content.
14. The method of claim 13, wherein the exhaust gas water content
is measured by a humidity sensor disposed in an exhaust passage of
the engine.
15. The method of claim 14, wherein the catalyst is positioned
upstream of the humidity sensor, and wherein the water storage and
release is determined based an amount of water produced during
combustion and catalyst temperature.
16. The method of claim 15, wherein the amount of water produced
during combustion is estimated based on intake air humidity,
air-fuel ratio, and fuel composition.
17. The method of claim 16, wherein the fuel composition is
determined based on output from the humidity sensor.
18. The method of claim 13, wherein adjusting the measured exhaust
gas water content further comprises, if water is being released
from the catalyst, decreasing the measured exhaust gas water
content by an amount of released water.
19. The method of claim 13, wherein adjusting the measured exhaust
gas water content further comprises, if water is being stored in
the catalyst, increasing the measured exhaust gas water content by
an amount of stored water.
20. The method of claim 13, wherein adjusting the fuel injection
amount further comprises increasing the fuel injection amount if
the adjusted exhaust gas water content is greater than a threshold,
and decreasing the fuel injection amount if the adjusted exhaust
gas water content is less than the threshold.
Description
FIELD
[0001] The present disclosure relates to an internal combustion
engine.
BACKGROUND AND SUMMARY
[0002] Exhaust gas sensors may be used to control a variety of
engine operating parameters. For example, U.S. Patent Application
No. 2011/0132340 describes detection of exhaust gas water content
using an exhaust gas sensor (e.g., a UEGO sensor), which is also
used to control engine air-fuel ratio. However, during the duration
in which the UEGO sensor is used to detect the exhaust water
content, the sensor does not measure the exhaust air/fuel ratio.
Therefore, during the water content detection period, the air/fuel
controllability is lost.
[0003] The inventors herein have recognized the issues with
utilizing an exhaust gas sensor to detect exhaust gas water
content. Accordingly, embodiments for providing a dedicated exhaust
gas water content sensor in an engine exhaust are provided. In one
embodiment, a method for an engine comprises, based on a dew point
of exhaust gas, adjusting an exhaust gas sensor heater configured
to heat an exhaust gas sensor disposed in an exhaust passage of the
engine, the dew point based on output from a humidity sensor
disposed in the exhaust passage.
[0004] In this way, a humidity sensor in the exhaust passage of the
engine may be used to determine the water content of the exhaust
(and hence the dew point), rather than other exhaust gas sensors.
By determining the dew point of the exhaust gas, the timing of
activating the exhaust gas sensor heater may be adjusted to avoid
rapid evaporation of condensate that has settled on the sensor when
the dew point is greater than the temperature of the sensor,
without compromising engine air-fuel ratio control. In some
examples, the humidity sensor may also be utilized to determine the
composition of the fuel used during combustion (e.g., ethanol
and/or water content of the fuel) and the light-off temperature of
a catalyst positioned in the engine exhaust. In doing so, accurate
air-fuel ratio may be maintained even as fuel composition changes,
and exhaust emissions may be controlled.
[0005] The above advantages and other advantages, and features of
the present description will be readily apparent from the following
Detailed Description when taken alone or in connection with the
accompanying drawings.
[0006] It should be understood that the summary above is provided
to introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined uniquely by the claims that follow
the detailed description. Furthermore, the claimed subject matter
is not limited to implementations that solve any disadvantages
noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a schematic diagram of an engine.
[0008] FIG. 2 is a flow chart illustrating a method for determining
exhaust gas water content according to an embodiment of the present
disclosure.
[0009] FIG. 3 is a flow chart illustrating a method for controlling
an exhaust gas sensor heater according to an embodiment of the
present disclosure.
[0010] FIG. 4 is a flow chart illustrating a method for correcting
humidity sensor output according to an embodiment of the present
disclosure.
[0011] FIG. 5 is a flow chart illustrating a method for diagnosing
a catalyst according to an embodiment of the present
disclosure.
[0012] FIG. 6 is a diagram illustrating engine operating parameters
during an engine cold start according to an embodiment of the
present disclosure.
[0013] FIG. 7 is a diagram illustrating engine operating parameters
during an engine cold start according to another embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0014] An exhaust humidity sensor may be used to determine or
adjust a variety of engine operating parameters. For example, the
humidity sensor output may indicate the alcohol or water content of
the combusted fuel, and engine fueling amounts during a cold start
may be adjusted based on the determined alcohol content. In another
example, the humidity sensor may be used to determine when to
activate an exhaust gas sensor heater to prevent cracking of the
sensor resulting from rapid evaporation of condensate on the
heater. The output of the humidity sensor may be affected by
changes in the exhaust gas water content due to a catalyst disposed
upstream of the humidity sensor. To compensate for these changes,
the output of the humidity sensor may be corrected based on
estimated stored or released water from the catalyst. These
estimated catalyst water amounts may also be used along with output
of the humidity sensor to determine the light-off temperature of
the catalyst. FIG. 1 is an engine including a humidity sensor
downstream of a catalyst and an engine controller, which may be
used to carry out the methods illustrated in FIGS. 2-5. FIGS. 6 and
7 illustrate various operating engine parameters during execution
of the above methods.
[0015] Referring specifically to FIG. 1, it includes a schematic
diagram showing one cylinder of multi-cylinder internal combustion
engine 10. Engine 10 may be controlled at least partially by a
control system including controller 12 and by input from a vehicle
operator 132 via an input device 130. In this example, input device
130 includes an accelerator pedal and a pedal position sensor 134
for generating a proportional pedal position signal PP.
[0016] Combustion cylinder 30 of engine 10 may include combustion
cylinder walls 32 with piston 36 positioned therein. Piston 36 may
be coupled to crankshaft 40 so that reciprocating motion of the
piston is translated into rotational motion of the crankshaft.
Crankshaft 40 may be coupled to at least one drive wheel of a
vehicle via an intermediate transmission system. Further, a starter
motor may be coupled to crankshaft 40 via a flywheel to enable a
starting operation of engine 10.
[0017] Combustion cylinder 30 may receive intake air from intake
manifold 44 via intake passage 42 and may exhaust combustion gases
via exhaust passage 48. Intake manifold 44 and exhaust passage 48
can selectively communicate with combustion cylinder 30 via
respective intake valve 52 and exhaust valve 54. In some
embodiments, combustion cylinder 30 may include two or more intake
valves and/or two or more exhaust valves.
[0018] In this example, intake valve 52 and exhaust valve 54 may be
controlled by cam actuation via respective cam actuation systems 51
and 53. Cam actuation systems 51 and 53 may each include one or
more cams and may utilize one or more of cam profile switching
(CPS), variable cam timing (VCT), variable valve timing (VVT)
and/or variable valve lift (VVL) systems that may be operated by
controller 12 to vary valve operation. The position of intake valve
52 and exhaust valve 54 may be determined by position sensors 55
and 57, respectively. In alternative embodiments, intake valve 52
and/or exhaust valve 54 may be controlled by electric valve
actuation. For example, cylinder 30 may alternatively include an
intake valve controlled via electric valve actuation and an exhaust
valve controlled via cam actuation including CPS and/or VCT
systems.
[0019] Fuel injector 66 is shown coupled directly to combustion
cylinder 30 for injecting fuel directly therein in proportion to
the pulse width of signal FPW received from controller 12 via
electronic driver 68. In this manner, fuel injector 66 provides
what is known as direct injection of fuel into combustion cylinder
30. The fuel injector may be mounted on the side of the combustion
cylinder or in the top of the combustion cylinder, for example.
Fuel may be delivered to fuel injector 66 by a fuel delivery system
(not shown) including a fuel tank, a fuel pump, and a fuel rail. In
some embodiments, combustion cylinder 30 may alternatively or
additionally include a fuel injector arranged in intake passage 42
in a configuration that provides what is known as port injection of
fuel into the intake port upstream of combustion cylinder 30.
[0020] Fuel tank in fuel system 172 may hold fuels with different
fuel qualities, such as different fuel compositions. These
differences may include different alcohol content, different
octane, different heats of vaporization, different fuel blends,
and/or combinations thereof etc. The engine may use an alcohol
containing fuel blend such as E85 (which is approximately 85%
ethanol and 15% gasoline) or M85 (which is approximately 85%
methanol and 15% gasoline). Alternatively, the engine may operate
with other ratios of gasoline and ethanol stored in the tank,
including 100% gasoline and 100% ethanol, and variable ratios
therebetween, depending on the alcohol content of fuel supplied by
the operator to the tank. Moreover, fuel characteristics of the
fuel tank may vary frequently. In one example, a driver may refill
the fuel tank with E85 one day, and E10 the next, and E50 the next.
As such, based on the level and composition of the fuel remaining
in the tank at the time of refilling, the fuel tank composition may
change dynamically.
[0021] The day to day variations in tank refilling can thus result
in frequently varying fuel composition of the fuel in fuel system
172, thereby affecting the fuel composition and/or fuel quality
delivered by injector 66. The different fuel compositions injected
by injector 66 may hereon be referred to as a fuel type. In one
example, the different fuel compositions may be qualitatively
described by their research octane number (RON) rating, alcohol
percentage, ethanol percentage, etc.
[0022] It will be appreciated that while in one embodiment, the
engine may be operated by injecting the variable fuel blend via a
direct injector, in alternate embodiments, the engine may be
operated by using two injectors and varying a relative amount of
injection from each injector. It will be further appreciated that
when operating the engine with a boost from a boosting device such
as a turbocharger or supercharger (not shown), the boosting limit
may be increased as an alcohol content of the variable fuel blend
is increased.
[0023] Intake passage 42 may include a charge motion control valve
(CMCV) 74 and a CMCV plate 72 and may also include a throttle 62
having a throttle plate 64. In this particular example, the
position of throttle plate 64 may be varied by controller 12 via a
signal provided to an electric motor or actuator included with
throttle 62, a configuration that may be referred to as electronic
throttle control (ETC). In this manner, throttle 62 may be operated
to vary the intake air provided to combustion cylinder 30 among
other engine combustion cylinders. Intake passage 42 may include a
mass air flow sensor 120 and a manifold air pressure sensor 122 for
providing respective signals MAF and MAP to controller 12.
[0024] Ignition system 88 can provide an ignition spark to
combustion chamber 30 via spark plug 92 in response to spark
advance signal SA from controller 12, under select operating modes.
Though spark ignition components are shown, in some embodiments,
combustion chamber 30 or one or more other combustion chambers of
engine 10 may be operated in a compression ignition mode, with or
without an ignition spark.
[0025] Exhaust gas sensor 126 is shown coupled to exhaust passage
48 upstream of catalytic converter 70 (also referred to simply as
catalyst 70). Sensor 126 may be any suitable sensor for providing
an indication of exhaust gas air/fuel ratio such as a linear oxygen
sensor or UEGO (universal or wide-range exhaust gas oxygen), a
two-state oxygen sensor or EGO, a HEGO (heated EGO), a NO.sub.x,
HC, or CO sensor. Exhaust gas sensor 126 may include a heater that
is configured to be activated when exhaust gas temperature is low,
in order to heat the exhaust gas sensor 126 to its operating
temperature. The exhaust system may include light-off catalysts and
underbody catalysts, as well as exhaust manifold, upstream and/or
downstream air-fuel ratio sensors. Catalytic converter 70 can
include multiple catalyst bricks, in one example. In another
example, multiple emission control devices, each with multiple
bricks, can be used. Catalytic converter 70 can be a three-way type
catalyst in one example.
[0026] A humidity sensor 128 may be disposed in exhaust passage 48.
As depicted in FIG. 1, humidity sensor 128 may be disposed
downstream of catalyst 70. However, other locations are possible,
such as upstream of catalyst 70. Humidity sensor 128 may measure
the relative humidity and temperature of the exhaust gas in exhaust
passage 48. Based on the relative humidity and temperature, the
specific humidity of the exhaust gas may be determined (e.g., the
amount of water per unit mass of exhaust flow). Output from
humidity sensor 128 may be sent to controller 12.
[0027] Controller 12 is shown in FIG. 1 as a microcomputer,
including microprocessor unit 102, input/output ports 104, an
electronic storage medium for executable programs and calibration
values shown as read only memory chip 106 in this particular
example, random access memory 108, keep alive memory 110, and a
data bus. The controller 12 may receive various signals and
information from sensors coupled to engine 10, in addition to those
signals previously discussed, including measurement of inducted
mass air flow (MAF) from mass air flow sensor 120; engine coolant
temperature (ECT) from temperature sensor 112 coupled to cooling
sleeve 114; a profile ignition pickup signal (PIP) from Hall effect
sensor 118 (or other type) coupled to crankshaft 40; throttle
position (TP) from a throttle position sensor; and absolute
manifold pressure signal, MAP, from sensor 122. Storage medium
read-only memory 106 can be programmed with computer readable data
representing instructions executable by processor 102 for
performing the methods described below as well as variations
thereof.
[0028] Storage medium read-only memory 106 can be programmed with
computer readable data representing instructions executable by
processor 102 for performing the methods described below as well as
other variants that are anticipated but not specifically listed. As
described above, FIG. 1 shows only one cylinder of a multi-cylinder
engine, and that each cylinder may similarly include its own set of
intake/exhaust valves, fuel injector, spark plug, etc.
[0029] Turning to FIG. 2, a method 200 for determining fuel
composition using a humidity sensor positioned in an engine exhaust
is illustrated. Method 200 may be carried out by an engine
controller (such as controller 12) according to instructions stored
thereon, in order to determine fuel alcohol content using a
humidity sensor (e.g., sensor 128). Method 200 may be performed
every time the engine is operated, or it may be performed only when
it is indicated that fuel composition be determined. For example,
method 200 may be carried out in response to a fuel tank refill
event. Method 200 optionally includes, at 202, determining a
baseline intake air humidity during non-fueling conditions. The
humidity sensor may output the relative humidity of the exhaust
gas, which may be used with the exhaust gas temperature to
determine the specific humidity of the exhaust gas (e.g., exhaust
gas water content). The amount of water in the exhaust gas reflects
not only the amount of alcohol and water in the fuel that is
combusted in the engine, but also the amount of water present in
the intake air. To determine the amount of water in the intake air,
the humidity sensor output may be collected during a non-fueling
condition. The non-fueling condition may include deceleration fuel
shut-off, where the engine temporarily operates without receiving
fuel during a deceleration event, prior to commencement of fuel
injection during an engine start, or other suitable condition.
However, instead of using the exhaust humidity sensor to determine
intake humidity during non-fueling conditions, a humidity sensor
may be present in the intake to determine the humidity of the
intake air during fueling conditions.
[0030] At 204, the exhaust gas water content is determined from the
exhaust humidity sensor output. As explained above, the exhaust
humidity sensor output may be used to determine the water content
of the exhaust gas. The water content indicates the amount of water
per unit mass of the exhaust gas, and thus, the mass air flow
through the engine and exhaust system is also determined to
calculate the exhaust gas water content. At 206, the exhaust gas
water content may be adjusted based on intake air humidity,
catalyst water storage, and/or other additional parameters that may
affect the exhaust gas water content determination. The exhaust gas
water content determined by the humidity sensor may be corrected to
remove the water content in the exhaust originating from the intake
air. In this way, the adjusted exhaust gas water content may only
reflect the amount of water resulting from the combusted fuel.
Further, if the humidity sensor is positioned downstream of an
exhaust catalyst or other aftertreatment device, the amount of
water stored in the catalyst or released from the catalyst during
the exhaust gas water content determination may be estimated to
compensate the humidity sensor reading for water stored or released
by the catalyst. For example, if the catalyst is storing water, the
output from the humidity sensor may indicate a lower exhaust gas
water content than is actually being produced by the engine.
Additional information regarding determining the amount of stored
or released water in the catalyst will be explained below with
respect to FIG. 4.
[0031] At 208, the fuel composition is determined based on the
exhaust gas water content. Fuel alcohol content may be mapped to
exhaust gas water content. For example, an exhaust gas water
content of around 83 g/Kg may indicate the engine is combusting
gasoline, while an exhaust gas water content of around 111 g/Kg may
indicate the engine is combusting a fuel blend of 85% ethanol and
15% gasoline. The controller may access a look-up table to
determine the fuel alcohol content. The fuel alcohol content
determined from the look-up table may be modified based on air-fuel
ratio or other parameters, in order to account for incomplete
combustion or other variables. Further, the amount of water in the
fuel may be determined under some conditions. For example, if the
engine is operating with 100% ethanol fuel, the amount of water in
the fuel may vary, and thus the humidity sensor may be used to
determine the water content of the fuel.
[0032] At 210, engine operating parameters may be adjusted based on
the determined fuel composition. Adjusted engine operating
parameters may include a fuel injection amount, spark timing, or
other parameters. In one example, the amount of fuel injected to
the engine during a cold engine start may be adjusted based on the
determined fuel alcohol content, in order to prevent under or
over-fueling that may lead to engine start issues or excessive
emissions. In one example, the fuel injection amount may be
increased if the exhaust gas water content is greater than a
threshold, and decreased if the exhaust gas water content is less
than the threshold. The threshold may be an expected amount of
exhaust gas water content (for example, an expected amount of water
produced by combusting a default fuel, such as gasoline). The
engine operating parameters may be adjusted immediately upon
determining the fuel composition. However, the fuel composition may
be stored in the memory of the controller, and the operating
parameters may be adjusted during subsequent engine operation.
[0033] Thus, method 200 provides for determining fuel composition
using an exhaust humidity sensor. The measured water content of the
exhaust gas may also be used to control the operation of a heater
configured to heat an exhaust gas sensor disposed in the exhaust
passage of the engine. FIG. 3 illustrates a method 300 for
controlling an exhaust gas sensor heater based on feedback from a
humidity sensor. The exhaust gas sensor heater may be positioned
near or in an exhaust gas sensor, and may be activated in order to
heat the sensor when the sensor is below its operating temperature.
The exhaust gas sensor may be an oxygen sensor used for air-fuel
ratio feedback control, such as sensor 126. If condensate has
settled on the sensor, when the heater is activated and the sensor
rapidly increases in temperature, evaporation of the condensate may
lead to cracking of the sensor. Thus, feedback from the humidity
sensor may indicate if condensate has likely collected on the
sensor, and if so, the heater may be controlled to prevent rapid
evaporation of the condensate.
[0034] Method 300 includes, at 302, determining engine operating
parameters. The engine operating parameters may include engine
temperature, exhaust gas temperature, whether the engine is
operating with cold start conditions, etc. At 304, it is determined
if the exhaust gas sensor is below its operating temperature. The
operating temperature may be the temperature at which the sensor
starts to function efficiently, determined by the manufacturer of
the exhaust gas sensor, and may be a fixed value such as
300.degree. C. The sensor may be heated by the exhaust gas;
however, the time lag associated with heating the sensor via the
exhaust may result in unsatisfactory air-fuel ratio control,
leading to increased emissions. To prevent this, a heating element
in the sensor may be activated to rapidly heat the sensor when it
is determined the sensor is below operating temperature.
Determining the sensor is below operating temperature may include
determining if the engine is operating with a cold engine start,
estimating the sensor temperature based on engine temperature or
exhaust gas temperature, or directly measuring sensor
temperature.
[0035] If it is determined the sensor is not below operating
temperature, method 300 proceeds to 306 to maintain current
operating parameters, and then method 300 returns. If the sensor is
below operating temperature, method 300 proceeds to 308 to
determine the dew point of the exhaust based on the humidity sensor
output. The dew point of the exhaust is the temperature below which
the water vapor exhaust will condense into liquid water, and may be
determined based on the relative humidity of the exhaust
(determined by the humidity sensor) and the exhaust pressure.
Determining the dew point may also include, at 310, adjusting the
humidity sensor output based on the amount of water stored or
released in a catalyst upstream of the humidity sensor. If a
catalyst or other exhaust component is disposed in the exhaust
passage between the exhaust gas sensor and the humidity sensor, the
relative humidity determined by the humidity sensor may not reflect
the relative humidity at the exhaust gas sensor due to water stored
by or released from the catalyst. Additional information about
determining the amount of stored or released water in the catalyst
is presented below with respect to FIG. 4.
[0036] At 312, it is determined if the dew point is less than the
exhaust gas sensor temperature. If the dew point is less than the
exhaust gas sensor temperature, condensate will not form on the
sensor, and thus method 300 proceeds to 316 to activate the heater.
However, if the dew point is not less than the exhaust gas sensor
temperature, condensate may form on the sensor. Thus, method 300
proceeds to 314 to deactivate the heater until the sensor
temperature exceeds the dew point. The sensor may be slowly heated
by the exhaust gas when the heater is deactivated. By waiting to
activate the heater until the temperature of the sensor is greater
than the dew point, rapid evaporation of the condensate on the
sensor may be avoided. However, in some embodiments, rather than
deactivating the heater, the heater may be adjusted to heat the
sensor more slowly than if no condensate was present.
[0037] Whether the heater is activated immediately at 316 or
whether the heater is deactivated until the exhaust gas sensor
temperature is greater than the dew point at 314, method 300
proceeds to 318 to determine if the sensor is at operating
temperature. If the sensor has not yet reached operating
temperature, method 300 loops back to 316 to continue to activate
the heater. If the sensor is at operating temperature, method 300
proceeds to 320 to deactivate the heater, and then method 300
returns.
[0038] Thus, the methods 200 and 300 of FIGS. 2 and 3 provide for
various parameter adjustments based on feedback from a humidity
sensor disposed in an exhaust passage of an engine. The humidity
reading output from the humidity sensor may be affected by a
catalyst upstream of the sensor, and thus the effect of the
catalyst on the downstream water content may be determined to
increase the accuracy of the humidity sensor readings. A catalyst
water storage model may be used to predict when the catalyst is
storing water, and how much water is stored in the catalyst.
Further, the catalyst water storage model may predict when and how
much water is released by the catalyst. By correcting the humidity
sensor output based on the stored/released water, the readings of
the humidity sensor used in the above methods may be of greater
accuracy. Further, as explained in more detail with respect to FIG.
5, the catalyst water storage model along with current output from
the humidity sensor may be used to diagnose degradation of the
catalyst.
[0039] FIG. 4 illustrates a method 400 for correcting a humidity
sensor using a catalyst water storage model. Method 400 may be
carried out by controller 12 to correct output from sensor 128
arranged downstream of catalyst 70. Method 400 includes, at 402,
determining engine operating parameters. The determined operating
parameters may include engine speed, engine load, exhaust
temperature, air-fuel ratio, elapsed time since an engine start,
and/or other parameters. At 404, the amount of water stored in the
catalyst is estimated. The amount of stored water may be estimated
based on a plurality of parameters. For example, the water content
of the exhaust upstream of the catalyst, pressure ratio across the
catalyst, and catalyst temperature may be used to predict whether
water is being stored in the catalyst. The water content of the
exhaust upstream of the catalyst may be estimated based on the
humidity of the intake air and water content produced during
combustion. The humidity of the intake air may be determined using
the exhaust humidity sensor during non-fueling conditions, or it
may be determined from an intake humidity sensor. The water content
produced during combustion may be based on air-fuel ratio, mass air
flow, and fuel composition (determined using method 200 of FIG. 2
in one example). Additionally, if the engine includes an exhaust
gas recirculation system that routes a portion of the exhaust gas
back to the intake of the engine, the humidity of the exhaust gas
and/or the amount of exhaust diverted away from the catalyst may
also be used to determine the stored water content.
[0040] Thus, the water storage in the catalyst may be determined by
estimating the water content of the exhaust, which is based on the
water content of the intake air and the water produced during
combustion. The amount of water that may accumulate in the catalyst
may then be determined based on the estimated water content and the
temperature of the catalyst (which may be directly measured or
estimated based on exhaust gas temperature), and in some
embodiments, also based on the pressure ratio across the catalyst.
However, in other embodiments, the amount of stored catalyst water
may be mapped to one or two simpler inputs, such as engine load and
catalyst temperature.
[0041] At 406, the amount of water released from the catalyst is
estimated. Depending on the temperature of the catalyst, the amount
of released water may be a function of catalyst temperature, the
amount of water previously stored in the catalyst (determined as
described above), and the mass flow of the exhaust through the
catalyst. For example, at catalyst temperatures below light-off,
the water being released (e.g., evaporated) from the catalyst may
be the water that has previously accumulated in the catalyst but is
now evaporating as the catalyst heats. However, around the
light-off temperature, constituents present in the exhaust gas
(e.g., NOx, unburnt hydrocarbons, CO) may be reduced in the
catalyst, releasing water as a byproduct of the reactions. Thus,
determining the amount of released water may include determining
both the amount of previously stored water currently being released
and the amount of water produced by the catalyst reactions. Whether
one or both of these water sources is being released is dependent
on the temperature of the catalyst. For example, below the
light-off temperature, nearly all the released water may be
evaporated water that had previously accumulated in the catalyst.
Then, by the time the catalyst reaches light-off temperature, all
the accumulated water may have evaporated, and thus the released
water may be water produced by the reactions occurring in the
catalyst.
[0042] The amount of water released by the reduction reactions of
the exhaust gas constituents may be determined based on air-fuel
ratio, engine load, and engine temperature, as well as catalyst
temperature. Additionally, if the amount of released water is being
determined following an engine cold start, the amount of water
released by the exhaust gas constituents may include reactions
occurring with constituents that have been stored in the catalyst
during cold catalyst operation (e.g., before light-off temperature
was reached). Thus, the specifics of the catalyst (such as type of
catalyst, size, etc.) as well as time since light-off temperature
was reached may also be used to determine the amount of released
water.
[0043] At 408, the humidity sensor output may be corrected based on
the water storage and release of the catalyst. For example, the
humidity sensor output may be corrected by the difference between
the estimated stored and released water. Thus, if more water is
being stored than released, the output of the humidity sensor may
be adjusted to reflect a higher-than-measured exhaust gas water
content. If more water is being released than stored, the output of
the humidity sensor may be adjusted to reflect a
lower-than-measured exhaust gas water content.
[0044] In this way, a catalyst water storage model may be used to
estimate at which catalyst temperatures water will be stored and/or
released from the catalyst in order to correct output from the
humidity sensor downstream of the catalyst. However, the catalyst
water storage model and output from the humidity sensor may also be
used to diagnose degradation of the catalyst. Specifically, as the
catalyst ages, it may take a longer amount of time to reach
light-off temperature, and/or the light-off temperature of the
catalyst may increase or otherwise change. The catalyst water
storage model may be used to predict when water is being stored and
when water is being released from the catalyst, and the output of
the humidity sensor may be used to determine if the water is
actually being stored and released as predicted. If a designated
amount of water is predicted to be released from the catalyst at
light-off temperature, but the humidity sensor indicates the water
is actually being released at a temperature higher than the
light-off temperature, for example, engine operating parameters may
be adjusted to compensate for the delayed light-off time.
[0045] FIG. 5 illustrates a method 500 for diagnosing a catalyst
using the catalyst water storage model and output from the humidity
sensor. Method 500 may be carried out by the controller 12 during a
suitable engine operating period, such as during and following an
engine cold start, where the catalyst temperature increases to
light-off temperature. Method 500 comprises, at 502, determining if
the catalyst below a threshold temperature. The threshold
temperature may be a designated catalyst light-off temperature (as
determined from the catalyst manufacturer or from a previous
diagnosis determination). If catalyst temperature is not below the
threshold, method 500 returns. If the catalyst is below the
threshold temperature, method 500 proceeds to 504 to predict the
amount of released water from the catalyst at the designated
light-off temperature. The amount of released water may be
predicting using the catalyst water storage model, explained above
with respect to FIG. 4, with an input of the designated light-off
temperature as the catalyst temperature used to estimate the amount
of released water. This amount of water is a prediction of the
water the catalyst will release once it reaches light-off
temperature. At 506, the exhaust gas temperature (or catalyst
temperature) at which the predicted amount of water is released is
determined. The amount of water actually released by the catalyst
may be determined by the humidity sensor. As the humidity sensor
outputs an indication of all the water content of the exhaust, the
humidity due to intake air and combustion may be removed from the
humidity sensor reading in one example.
[0046] At 508, it is determined if the exhaust gas temperature at
which the predicted amount of water is actually released is
different than the designated light-off temperature. The term
"different than" may include any temperatures that are different
than the light-off temperature. However, in other embodiments, the
measured exhaust gas temperature may be different than the
light-off temperature by more than a threshold amount, such as
within 10.degree. C. of the light-off temperature. Similarly, when
determining at which temperature the actual amount of water
released from the catalyst is equal to the predicted amount, equal
to may include the exact same amounts, or it may include within a
threshold range, such as within 5% of the predicted amount. If the
exhaust gas temperature is not different than the designated
light-off temperature, method 500 proceeds to 510 to maintain
current operating parameters (as the determined light-off
temperature is equal to the designated light-off temperature), and
method 500 returns.
[0047] If the exhaust gas temperature is different than the
designated light-off temperature, method 500 proceeds to 512 to set
the actual light-off temperature of the catalyst as being equal to
the measured exhaust gas temperature at which the predicted amount
of water was released. At 514, engine operating parameters may be
adjusted based on the newly-set light-off temperature. This may
include, at a subsequent cold start, increasing the exhaust gas
temperature to a higher temperature, increasing the exhaust
temperature more quickly, etc., than when operating with the
designated light-off temperature. Because the catalyst is operating
with a different light-off temperature than previous operations, to
prevent increased exhaust emissions, the catalyst is heated to the
new light-off temperature by the exhaust gas. To increase the
exhaust temperature more quickly or to a higher temperature, spark
timing may be retarded, air-fuel ratio may be adjusted, an engine
cooling circuit may be adjusted, etc. For example, the engine
cooling circuit may include a valve controllable to adjust the
amount of coolant cooled by an engine heat exchanger. To heat the
exhaust, the amount of coolant that is cooled may be reduced, thus
causing a rise in engine and exhaust temperatures. Other operating
parameters may also be adjusted, such as the boost pressure of the
engine (if the engine is turbocharged), amount of exhaust gas
recirculation, etc. Further, if the light-off temperature of the
catalyst has changed by a relatively large amount, an operator may
be notified that the catalyst is degraded.
[0048] Thus, method 500 of FIG. 5 may diagnose a catalyst light-off
temperature by comparing the humidity of the exhaust gas to an
expected exhaust gas humidity at catalyst light-off temperature. If
the humidities are not equal (or within a threshold range, such as
5%), it may be determined that the catalyst is not operating with
the expected catalyst light-off temperature. To prevent increased
emissions when the light-off temperature is different than
expected, engine operating parameters may be adjusted. For example,
spark timing may be retarded and/or air-fuel ratio increased to
increase exhaust gas temperature to the new light-off
temperature.
[0049] FIGS. 6 and 7 illustrate various engine operating parameters
during execution of the above-described methods in a flex-fuel
vehicle configured to operate with varying types of fuel. For
example, the vehicle may operate with gasoline fuel and on a
subsequent tank refill, may operate with E85 fuel. Specifically,
diagram 600 of FIG. 6 illustrates exhaust temperature, fuel alcohol
content, exhaust humidity, exhaust gas sensor heater operation, and
catalyst water storage level during an engine cold start (e.g.,
when the engine is operating from ambient temperature at start-up)
with gasoline fuel. Diagram 700 of FIG. 7 illustrates exhaust
temperature, fuel alcohol content, exhaust humidity, exhaust gas
sensor heater operation, and catalyst water storage level during an
engine cold start with E85 fuel (85% ethanol, 15% gasoline). For
each diagram, time is illustrated on the horizontal axis, while
each respective operating parameter is illustrated on the vertical
axis.
[0050] Referring first to FIG. 6, exhaust temperature during the
cold start is illustrated by curve 602. At start-up, the engine may
be operating with relatively low exhaust temperature, such as
ambient temperature. As the engine warms up, exhaust temperature
also increases. The engine is operating with gasoline fuel (or a
fuel that otherwise is comprised of little to no alcohol). As shown
by curve 604, the fuel alcohol content of the fuel injected to the
engine is 0%.
[0051] Further, as depicted by curve 606, exhaust humidity
(measured by humidity sensor 128) remains relatively constant
during the initial stage of the cold start (before time T.sub.1).
Also during the beginning of the time depicted in diagram 600, the
dew point is greater than the temperature of the exhaust gas sensor
(which may be at a relatively similar temperature as the exhaust),
and thus the exhaust gas sensor heater is off, as illustrated by
curve 608. However, at time T.sub.1, the temperature of the exhaust
gas sensor increases above the dew point, and the heater is turned
on.
[0052] The engine may also include a catalyst in the exhaust
passage. When the catalyst is cold immediately following the engine
start, it may store water (e.g., condensate may accumulate within
the catalyst). Thus, as shown by curve 610, the amount of water
stored in the catalyst may gradually increase as the humid exhaust
travels through the catalyst. However, as the catalyst begins to
warm due to the increasing temperature of the exhaust, the amount
of condensate that accumulates in the catalyst may decrease. At
time T.sub.3, the exhaust temperature may be sufficiently high (and
be flowing at a sufficiently high velocity) to heat the catalyst to
a point where the stored water begins to be released (e.g., the
condensate beings to evaporate). As a result, the amount of stored
water in the catalyst begins to decrease until no water remains in
the catalyst. The released water from the catalyst may be reflected
in the exhaust humidity measured by the humidity sensor, which as
shown in curve 606, increases after time T.sub.3 as the catalyst
water is released.
[0053] Further, because the catalyst is storing water during most
of the duration of time depicted by diagram 600, the exhaust
humidity determined by the humidity sensor may be inaccurate if the
humidity sensor is disposed downstream of the catalyst. For
example, the water stored in the catalyst is not reaching the
humidity sensor, and thus the sensor may be outputting a lower
humidity level than the actual humidity upstream of the catalyst.
As explained earlier, if the amount of water stored in the catalyst
is known (for example, if it is estimated using the catalyst water
storage model), the exhaust humidity determined by the sensor may
be corrected to account for the catalyst water storage.
[0054] Referring now to FIG. 7, exhaust gas temperature,
illustrated by curve 702, starts low and rises as the engine warms
up during the cold start. The engine is injecting E85 fuel, and as
such the fuel alcohol content illustrated by curve 704 is at
approximately 85%. Because E85 fuel produces more water during
combustion than gasoline fuel, the exhaust humidity depicted in
curve 706 is higher than the exhaust humidity depicted by curve 606
of FIG. 6. Due to the higher amount of exhaust humidity, the dew
point of the exhaust may be higher, and as such the exhaust
temperature may increase to a higher temperature before the heater
is turned on than when the engine operates with gasoline fuel.
Thus, the exhaust gas sensor heater, illustrated by curve 708, is
turned on at time T.sub.2, which is delayed compared to when the
exhaust gas sensor heater was activated in diagram 600.
Additionally, the amount of water stored in the catalyst is greater
when operating with E85 fuel than with gasoline fuel, which is
illustrated in curve 710. However, similar to the water storage
illustrated in FIG. 6, once the exhaust temperature reaches a high
enough temperature, the water in the catalyst is released after
time T.sub.3, and the exhaust humidity increases.
[0055] It will be appreciated that the configurations and methods
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and non-obvious combinations and sub-combinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0056] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
* * * * *